Orbital, Superhump, and Superorbital Periods in the Cataclysmic Variables AQ Mensae and IM Eridani

TL;DR

This study detects orbital, superorbital, and sideband signals in the light curves of AQ Mensae and IM Eridani, indicating tilted accretion discs, and discusses the implications for understanding disc precession in cataclysmic variables.

Contribution

First detection of multiple periodic signals indicating disc tilt in AQ Mensae and IM Eridani, expanding knowledge of tilt phenomena in cataclysmic variables.

Findings

Detection of orbital, superorbital, and sideband signals in both systems.

AQ Mensae is an eclipsing system with variable eclipse depths.

Evidence supports the presence of tilted accretion discs in these CVs.

Abstract

We report photometric detections of orbital and superorbital signals, and negative orbital sidebands, in the light curves of the nova-like cataclysmic variables AQ Mensae and IM Eridani. The frequencies of the orbital, superorbital, and sideband signals are 7.0686 (3), 0.263 (3), and 7.332 (3) cycles per day (c/d) in AQ Mensae, and 6.870 (1), 0.354 (7), and 7.226 (1) c/d in IM Eridani. We also find a spectroscopic orbital frequency in IM Eridani of 6.86649 (2) c/d. These observations can be reproduced by invoking an accretion disc that is tilted with respect to the orbital plane. This model works well for X-ray binaries, in which irradiation by a primary neutron star can account for the disc's tilt. A likely tilt mechanism has yet to be identified in CVs, yet the growing collection of observational evidence indicates that the phenomenon of tilt is indeed at work in this class of object. The results presented in this paper bring the number of CVs known to display signals associated with retrograde disc precession to twelve. We also find AQ Mensae to be an eclipsing system. The eclipse depths are highly variable, which suggests that the eclipses are grazing. This finding raises the possibility of probing variations in disc tilt by studying systematic variations in the eclipse profile.